The isopiestic molalities and the water activities were measured at 298.15 K for the LiCi-Li2B4O7-H2O system by isopiestic method, and the vapor pressures and the osmotic coefficients were obtained from the measurements. The experimental data were represented by different forms of the ion interaction model based on the primary Pitzer model of osmotic coefficient. The Pitzer ion interaction parameters were, evaluated from recent measurements by using multiple regression and iterative method. The activity coefficients of LiCl and Li2B4O7 for the system LiCl-Li2B4O7-H2O were calculated by the ion interaction model parameterized at low concentrations. The data of osmotic coefficients measured are in reasonable agreements with those calculated by using the model. These studies are useful to improve the thermodynamic model for salt lake brine systems containing lithium and borates. The isopiestic molalities and the water activities were measured at 298.15 K for the LiCi-Li2B4O7-H2O system by isopiestic method, and the vapor pressures and the osmotic coefficients were obtained from the measurements. The experimental data were represented by different forms of the ion interaction model based on the primary Pitzer model of osmotic coefficient. The Pitzer ion interaction parameters were, evaluated from recent measurements by using multiple regression and iterative method. The activity coefficients of LiCl and Li2B4O7 for the system LiCl-Li2B4O7-H2O were calculated by the ion interaction model parameterized at low concentrations. The data of osmotic coefficients measured are in reasonable agreements with those calculated by using the model. These studies are useful to improve the thermodynamic model for salt lake brine systems containing lithium and borates.